Chapter 1. Red Hat Cluster Manager Overview

Red Hat Cluster Manager allows administrators to connect separate systems (called members or nodes) together to create failover clusters that ensure application availability and data integrity under several failure conditions. Administrators can use Red Hat Cluster Manager with database applications, file sharing services, web servers, and more.

To set up a failover cluster, you must connect the member systems (often referred to simply as members or nodes) to the cluster hardware, and configure the members into the cluster environment. The foundation of a cluster is an advanced host membership algorithm. This algorithm ensures that the cluster maintains complete data integrity at all times by using the following methods of inter-member communication:

To make an application and data highly available in a cluster, you must configure a service (such as an application and shared disk storage) as a discrete, named group of properties and resources to which you can assign an IP address to provide transparent client access. For example, you can set up a service that provides clients with access to highly-available database application data.

You can associate a service with a failover domain, a subset of cluster members that are eligible to run the service. In general, any eligible member can run the service and access the service data on shared disk storage. However, each service can run on only one cluster member at a time, in order to maintain data integrity. You can specify whether or not the members in a failover domain are ordered by preference. You can also specify whether or not a service is restricted to run only on members of its associated failover domain. (When associated with an unrestricted failover domain, a service can be started on any cluster member in the event no member of the failover domain is available.)

You can set up an active-active configuration in which the members run different services, or a hot-standby configuration in which a primary member runs all the services, and a backup cluster system takes over only if the primary system fails.

Figure 1-1 shows an example of a cluster in an active-active configuration.

Figure 1-1. Example Cluster in Active-Active Configuration

If a hardware or software failure occurs, the cluster automatically restarts the failed member's services on the functional member. This service failover capability ensures that no data is lost, and there is little disruption to users. When the failed member recovers, the cluster can re-balance the services across the members.

In addition, you can cleanly stop the services running on a cluster system and then restart them on another system. This service relocation capability allows you to maintain application and data availability when a cluster member requires maintenance.

1.1. Red Hat Cluster Manager Features

Cluster systems deployed with Red Hat Cluster Manager include the following features: